1. Field of the Invention
The present invention relates generally to optical fibers, and particularly to optical fibers with airline features, and to a method of manufacturing such fibers.
2. Technical Background
Corning, Inc introduced a new optical fiber, ClearCurve® optical fiber, in 2007. This fiber has improved bend performance due to gas filled voids randomly situated in an annular region surrounding the core of the fiber. The gas filled voids are randomly distributed and are created by trapping gas in the soot during sintering of the preform. The gas filled voids are elongated as the preform is drawn into fiber. These gas filled voids do not extend over the entire length of the fiber and are typically less than 10 m in length.
Photonic crystal fibers and photonic band gap fibers (PCFs and PBGFs) are usually created by a “stack and draw” method. The term “stack and draw” refers to assembling a preform from constituent parts using, for example, small tubes and/or rods with round or hexagonal cross-sections, and stacking them together in a precise orientation. These stacked components are usually situated inside an overclad tube. The overclad tube with the stacked components is then either collapsed and pulled into intermediate preform parts, or directly drawn into an optical fiber. The preform may also be etched to enlarge the inside diameters of the small tubes in order to change the ratio of glass to air in a cross section of the preform, to enhance optical properties of the fiber.
PCFs and PBGFs are expensive to make, because in order to propagate light properly, they require a great amount of precision in placement of different preform components (e.g., core rod(s), and the glass tubes surrounding the core rod(s). The preform components such as the overclad tube and the small glass tubes surrounding the core rod(s) are typically expensive and contribute to the cost of making these fibers. In addition, PCFs and PBGFs are expensive due to the relatively small amount of fiber resulting per preform assembly (when compared to a standard optical transmission fiber preform making processes), resulting from the relatively small size of the optical preforms.